The present invention is concerned with the detection of ships, and more specifically with the avoidance of detection of a ship by an infrared detector.
The most common means of guiding a missle onto a moving target are radar and heat-seeking devices. These latter guidance systems detect the infrared radiation emitted by all bodes above absolute zero, and then "home" in on the strongest source. When the target is a ship at sea, the job is made easier by the fact that the background, the ocean, is at a relatively constant temperature. Thus, it is easy for the detection system to pick out a ship, which is at a higher temperature than the ocean, against the relatively "flat" background.
Radar systems can be confused by dropping small pieces of metal foil, called "chaff", between the radar set and the target. The radar signals bounce off the chaff and show on the screen as a large blur. Attempting to confuse a heat-seeking guidance system in a similar manner is obviously impractical, since it would require large quantities of fuel to produce sufficiently large amounts of infrared radiation. Therefore, the only realistic way to avoid detection of a ship by a heat-seeking device is to reduce the temperature of all parts of the ship to that of the background, or to approach this temperature as nearly as possible.
On a ship, the highest external temperature exists in the stack gases and the smokestack itself. The smokestack and gases are considerably higher in temperature than the rest of the ship, hence, the heat-seeking guidance system would lock onto these sources and head for the ship. Therefore, it is necessary to cool the smokestack and gases.
The prior art shows an unrealistic and unworkable scheme for entirely eliminating a ship's exhaust by washing the soot particles out of it and discharging the cleaned and cooled gases at sea level. However, no workable prior art was found relating to the cooling of the smokestack and gases to eliminate infrared radiation.